1. Technical Field
The present disclosure relates to an image capturing device; in particular, to an automatic focusing method executed in the image capturing device which has a plurality of cameras, and an automatic focusing device and the image capturing device which use the automatic focusing method.
2. Description of Related Art
The current image capturing device is usually a digital image capturing device, which can automatically find a focus distance by using at least one of the software, hardware, firmware, such that a photographer can take a picture which has a clear scene. Referring to FIG. 1, FIG. 1 is a curve diagram showing a focusing evaluation value and a step movement index after the conventional automatic focusing method executed in the image capturing device with a single one lens module moves the lens module each time. The conventional automatic focusing method gradually moves the lens module to adjust the focus distance of the lens module and obtain the corresponding focusing evaluation value, such as the contrast or clarity of the image. The conventional automatic focusing method can find the focus distance corresponding to the maximum focusing evaluation value after gradually moving the lens module several times, and the focus distance corresponding to the maximum focusing evaluation value may be the correct focus distance.
In FIG. 1, during the procedure of the first seven lens module movements, the focusing evaluation value which is obtained after the lens module moves current time is larger than the focusing evaluation value which is obtained after the lens module moves previous time. However, the focusing evaluation value which is obtained after the lens module moves eighth time is less than the focusing evaluation value which is obtained after the lens module moves seventh time. The conventional automatic focusing method considers that the focus distance corresponding to the seventh lens module movement may be the correct focus distance corresponding to the scene currently captured by image capturing device, and thus sets the focus distance corresponding to the seventh lens module movement to the focus distance which the image capturing device can capture the scene currently, so as to finish the procedures of the conventional automatic focusing method. It is noted that, the automatic focusing method in the example must capture eight images, and thus the speed for automatic focusing is not fast. In addition, since the conventional automatic focusing method must move the lens module several times, the movement deviation of the actuator is accumulated during the automatic focusing procedure.